MBM 12: young protoplanetary discs at high galactic latitude

TL;DR

This study uses Spitzer infrared data to analyze dust evolution and disc clearing in young T Tauri stars within the high-latitude MBM 12 cloud, revealing spatial dust composition gradients and rapid inner disc clearing.

Contribution

It introduces a new spectral decomposition method (TLTD) for analyzing IRS spectra and provides detailed dust property measurements in MBM 12's protoplanetary discs.

Findings

Radial gradient in forsterite to enstatite ratio indicating limited radial mixing.

Discs show rapid inner clearing, especially in binary systems.

Dust properties are mildly related to disc characteristics, independent of stellar type.

Abstract

(abridged) We present Spitzer infrared observations to constrain disc and dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12 T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line and the rest classical T Tauri stars. We first use MIPS and literature photometry to compile spectral energy distributions for each of the 12 members in MBM 12, and derive their IR excesses. The IRS spectra are analysed with the newly developed two-layer temperature distribution (TLTD) spectral decomposition method. For the 7 T Tauri stars with a detected IR excess, we analyse their solid-state features to derive dust properties such as mass-averaged grain size, composition and crystallinity. We find a spatial gradient in the forsterite to enstatite range, with more enstatite present in the warmer regions. The fact that we see a radial dependence of the dust properties indicates that radial mixing is not very efficient in the discs of these young T Tauri stars. The SED analysis shows that the discs in MBM 12, in general, undergo rapid inner disc clearing, while the binary sources have faster discevolution. The dust grains seem to evolve independently from the stellar properties, but are mildly related to disc properties such as flaring and accretion rates.